Nizolda oquvchi avtomatlarini ishlab chiqishida qanday narsalarga e'tibor berish kerak?

Pastga o'rnatilgan past ma'lumotli avtomatik klyuchlar, elektr tarmog'ida muhim himoya va boshqarish qurilmalari hisoblanadi. Ularning dizayni va ishlash tartibi tizimning xavfsizligi va ishonchiligiga toliq ta'sir qiladi. Dizayn jarayonida mohiyat moslash, elektr parametrlari orasidagi moslash va aktivator tanlanishi to'g'ridan-to'g'ri bir necha sharoitlarda barqaror ishlashini ta'minlaydi. Ishlash jarayonida, xavfsizlik protokollariga rang-rang rioya qilish, muddatli yaxlitish va noqulay holatlarni to'g'ri boshqarish talab etiladi, bu esa noto'g'ri ishlatishdan kelib chiqqan kazalardan saqlanishga yordam beradi. Bu maqola past ma'lumotli avtomatik klyuchlar uchun asosiy dizayn printsiplari va ish rejalarini sistemalashtirib, inshoot ishchilariga mutaxassit yo'nalish beradi.

1. Past ma'lumotli avtomatik klyuchlar uchun dizayn e'tibollar

Past ma'lumotli avtomatik klyuchlar dizayni qattiq tashqi mohiyatga davom etish va himoya va boshqarish talablarni qanoatlantirish kerak.

1.1 Mohiya moslash

Bu qurilmalar, tashqi o'rnatilgan ekanligi sababli, harorat o'zgarishlari, namlik, tuzli yog' toshqinlari va mexanik titrebishlarga qarshi davolash kerak. GB/T 2423.17 bo'yicha, ular 72 soatlik neutral tuzli yog' toshqin sinovidan (5-daraja) o'tish kerak, bu esa deyarli qirg'oq yoki sanoat hududlarida mos keladi, zira 3- darajadagi zanjirlanish darajasi konduktor zanjirlanishiga yoki kondensatsiyaga qarshi ko'nikuv qiladi. Yuqori maydonlar (>2000m) uchun, izolyatsiya va harorat oshish parametrlari GB/T 20645-2021 bo'yicha o'zgartirilishi kerak (har 100m oshishda harorat cheklovini 1% pasaytirish; 4000m dan yuqoriga o'tishda tebranish miqdori kamaytirilishi kerak).

Past harorat uchun, -40°C da ishlash va -55°C da saqlash ta'minlanishi, shuningdek, ishonchli aktivator ishlashi kerak. UV nisbatiga qarshi, poliamid boyali (kontakt burchagi >90°) yoki PVDF (UV eskirish nisbati ≥ 8-daraja) kabi yuz qiymatlari talab etiladi. Qutining yopish IP54/55 standartlariga javob berishi kerak, bu esa izolyatsiya pasayishidan himoya qiladi.

1.2 Elektr parametrlari orasidagi moslash

To'g'ri tortish araligini hisoblash va to'g'ri parametrlarni tanlash muhimdir. Tortish araligi absolyut usulda, uch fazadan, ikki fazadan va bir fazada yer bilan bog'liq tortish araligini hisobga olgan holda hisoblanishi kerak. Boshlang'ich uch fazali tortish araligi quyidagicha hisoblanadi:

bu yerda Un - nominal liniya harorati, R_k, X_k - tortish araligi umumiy qarshilik va reaktivlik. Avtomatik klyuchning belgilangan tortish araligi (Ics) eng katta uch fazali tortish araligidan kamroq bo'lishi mumkin emas. Chuvstvaniylik tekshirish uchun liniya oxiridagi minimal tortish araligi aniq vaqtli yoki qisqa muddatli yuqori tebranish deb band qilish sozlamasidan kamida 1.3 marta bo'lishi kerak: I_min≥1.3I_set3.

Yuk ostida himoyasi uchun, uzun muddatli yuqori tebranish sozlamasi Iset1 quyidagicha qanoatlantirishi kerak: I_z≥I_set1≥I_c, bu yerda Iz - konsultatsiya doimiy tebranish qobiliyati va IcIc - hisoblangan yuk tebranish miqdori. Tortish himoyasi uchun, aniq vaqtli yuqori tebranish sozlamasi I_set3 eng katta motorning (masalan, sigir suruvchan motorlar uchun 20-35 marta nominal tebranish) to'liq ishga tushish tebranishidan kamida 1.2 marta yuqori bo'lishi kerak, qisqa muddatli sozlamasi I_set2 esa vorpal yuk qutilarini oldini olish uchun, adolatli ravishda 1.2 marta (eng katta motorning ishga tushish tebranishi + boshqa yuk tebranishlari) sozlanishi kerak.

1.3 Aktivator tanlovi

Spring-operated mechanisms are commonly used, requiring reliability, anti-jump, free-tripping, and buffering functions. Timing parameters: frame breakers—closing ≤0.2s, opening ≤0.1s; molded-case breakers—mechanical life ≥10,000 operations (frame breakers ≥20,000). The actuator must include energy storage detection and interlocking for safe operation. Dynamic characteristics require optimized contact speed and displacement control (e.g., staged control for vacuum breakers to minimize contact bounce). Output characteristics must match the breaker to ensure closure under short-circuit conditions. In cold regions, capacitor ESR increases at -40°C, prolonging closing time; variable-temperature testing is essential.

2. Himoya funktsiyalari dizayni va sozlamalar tanlovi

2.1 Yuk ostida himoya

Typically implemented via thermal-magnetic or electronic trip units. Thermal-magnetic units use bimetallic strips with inverse-time characteristics (trip time inversely proportional to the square of overload current). Electronic units offer precise control, with long-time trip settings Ir ranging from 0.4 to 1 times the rated current In. Settings must satisfy In≥Ic and In≤Iz. Sensitivity: Sp=I_kmin/I_op≥1.3, where IkminIkmin is the minimum single-phase short-circuit current at the line end. For critical loads, overload protection may trigger alarms instead of tripping.

2.2 Short-Circuit Protection

Includes short-time and instantaneous protection. Short-time protection ensures selectivity: $\×$ (max motor starting current + other loads), with time delays (0.1–0.4s) coordinated with upstream breakers (≥0.1–0.2s time difference). Instantaneous protection targets severe faults: $\×$ full motor starting current (e.g., 12–18 times InIn for motors). For distribution feeders, electronic trip units with delayed instantaneous protection are preferred. Selectivity: upstream short-time setting ≥1.3 × downstream instantaneous setting, with ≥0.1–0.2s time delay difference.

2.3 Undervoltage Protection

Prevents equipment damage from voltage sags. Trip range: 35%–70% of rated voltage. Instantaneous types trip immediately but may cause nuisance tripping; delayed types (0–5s) ignore transient fluctuations, suitable for industrial use. The undervoltage trip unit’s rated voltage must match the line voltage, and its function must not interfere with other protections. Delayed types (0.2–3s) are recommended for industrial applications.

3. Selectivity Coordination and Cascading Protection

3.1 Selectivity Zones

• Zone 1 (Isc < downstream Icu): Achieved via current and time grading (e.g., upstream $\&times;$ downstream Iset3Iset3, time delay &ge; downstream + 0.1s).

• Zone 2 (downstream Icu < Isc < upstream Icu): Relies on current-limiting characteristics or manufacturer data. Selectivity limit IsIs may be less than downstream Icu (partial selectivity).

• Zone 3 (Isc > upstream Icu): Requires testing; upstream contacts may momentarily open (&le;30ms) without tripping, provided no welding occurs.

3.2 Cascading Protection

Leverages upstream breaker current-limiting to allow use of lower-breaking-capacity downstream breakers, reducing cost. Requires matching instantaneous settings and avoiding critical loads on cascaded circuits. Energy-based selectivity (e.g., in A-type breakers) can enhance selectivity limits, but verification via manufacturer data is essential.

3.3 Selectivity Methods

• Current Selectivity: Upstream instantaneous setting &ge;1.3 &times; downstream.

• Time Selectivity: Upstream short-time delay &ge; downstream + 0.1&ndash;0.2s.

• Energy Selectivity: Based on contact system energy requirements.

• Logic Selectivity: Downstream fault detection sends a lockout signal to upstream, enabling fast downstream tripping while upstream remains closed&mdash;ensuring "stable, accurate, fast" protection.